Tool fixing device in a tool holder

ABSTRACT

A tool fixing device for clamping a tool in a tool holder, wherein the tool holder has a receptacle configured to clamp a shaft of the tool, has at least one static flexible element inserted into a force flow between the tool and the tool holder. The static flexible element is designed to damp tilting and bending vibrations of the tool in cooperation with a damping element provided in the receptacle at the free end of the shaft of the tool. This prevents chattering of the tool.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a tool fixing device in a tool holder in whosereceptacle a shaft of the tool is clamped.

2. Description of the Related Art

In known tool fixing devices (FIG. 2) a shaft 4 of a tool 1 is clampedrigidly in a receptacle 3 of a tool holder 2 by means of a clampingmember 9 seated in the tool holder 2. Slim tools, for example, endmilling cutters or boring bars, often produce vibration amplitudesduring machining because of their minimal flexural strength and systemdamping action which vibration amplitudes in most cases occur in theform of a regenerative chatter. These vibrations can only be avoided byreducing the cutting depth of the tool. Slim end milling cutters are,for example, used for milling pockets, for milling deep-drawing andforging tools as well as for producing integral components for aircraftconstruction. The load or performance limit is the chatter tendency ofthe tool as a result of its minimally damped bending vibration.

However, boring operations with boring bars having a length/diameterratio >4 are also limited in regard to their efficiency as a result oftheir chatter tendency. This holds true for stationary drilling tools onturning machines as well as for rotating boring tools on horizontalboring mills and milling machines.

SUMMARY OF THE INVENTION

The invention has the object to design the fixing device of theaforementioned kind such that the chatter vibrations during machining ofa workpiece can be prevented without reducing the load or efficiencylimits of the tool.

In accordance with the invention, this object is solved for the fixingdevice of the aforementioned kind in that in the force flow between thetool and the tool holder at least one static flexible element isinserted which has a high damping action.

In the fixing device according to the invention at least one staticflexible element which has a high damping action is inserted into theforce flow between the tool and the tool holder. As a result of thisdamped clamping action, the tool can yield in a springy way relative tothe tool holder. As a result of the high damping action, the tool doesnot chatter even when it has a great length and/or is very slim. Thecorresponding damping element is mounted at the location of greatestrelative movement between the shaft end of the tool and the tool holder.As a result of the fixing device according to the invention, the toolshaft can perform a tilting movement about its clamping location whichserves as a pivot point.

Further features of the invention result from, the description and thedrawings.

BRIEF DESCRIPTION OF THE DRAWING

The invention will be explained in more detail with the aid of twoembodiments illustrated in the drawings. It is shown in:

FIG. 1a schematic illustration of a tool fixing device according to theinvention;

FIG. 2a tool fixing device of the prior art in an illustrationcorresponding to that of FIG. 1;

FIG. 3 and FIG. 4 three different embodiments of the tool fixing deviceaccording to the invention in axial section; and

FIG. 3a a view similar to FIG. 3, showing an elastic ring in a groove ofthe sleeve;

FIG. 5 a comparison of the properties of the tool fixing deviceaccording to the prior art and of the tool fixing device according tothe invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 show schematically a tool 1 which is received in a tool holder 2.The tool 1 can be, for example, an end milling cutter, a boring bar andthe like. The tool holder 2 can be embodied as a quick-release taper,HSK, VDI shaft, and the like. The tool 1 is received via the tool holder2 in a spindle (not illustrated) with which the tool 1 can be driven inrotation. The tool holder 2 has a cylindrical receptacle 3 into whichthe shaft 4 of the tool 1 projects. A static flexible element 5 that hasa directed high damping action 8 is inserted into the force flow betweentool 1 and tool holder 2. The tool shaft 4 tilts about a springyclamping location (pivot point). In this connection, the free shaft endis radially deflected the farthest. At least one damping element 8 isprovided on this location of greatest relative movement between theshaft end 6 and the inner wall 7 of the receptacle 3. It isadvantageously a squeeze-film damper but can also be, for example, arubber damper, for example, in the form of an O-ring. By means of astatic flexible element 5, which can also be a membrane spring, a spiralspring or another elastic element, the tool shaft 4 is clamped in asoft-sprung fashion in the tool holder 2. The tool shaft 4, and thus thetool 1, can accordingly perform a tilting movement about this clampinglocation that serves as a pivot point.

FIG. 3 shows a first embodiment of such a tool fixing device. The shaft4 of the tool 1 is received in a sleeve 9 which is detachably fastenedby means of a radially outwardly projecting flange 10 on the end face ofthe tool holder 2. In the sleeve 9 a depression 11 is provided at thefree end and surrounds the shaft 4 at a minimal spacing. The depressionis open toward the end face of the sleeve 9.

Within the receptacle 3 of the tool holder 2 the sleeve is surrounded byan annular space 12 in which a pressure medium 13, preferably oil, ispresent The annular space 12 is limited radially outwardly by the innerwall of the receptacle 3. The annular space 12 extends minimally pastthe tool holder 2 into the flange 10 of the sleeve 9.

The sleeve 9 has a bottom 15 positioned opposite the bottom 14 of thereceptacle 3 at a minimal axial spacing. Starting at the bottom 15, theouter diameter of the sleeve 9 is reduced so that a circumferentialdepression 16 open toward the bottom 15 is formed in which a ring 17 ispositioned. The outer diameter of the ring 17 is slightly smaller thanthe inner diameter of the receptacle 3 so that between the ring 17 andthe inner wall of the receptacle 3 a narrow, annular damping gap 18 isformed which is in communication with the annular space 12 and in whichpressure medium is present also. The ring 17 rests against a radiallyoutwardly oriented annular shoulder 19 of the sleeve 9 and projectsradially past the outer wall of the sleeve. Accordingly, the annularspace 12 is radially wider than the damping gap 18.

Since the annular space 12 extends axially slightly past the tool holder2 into the flange 10 of the sleeve 9, a narrow annular stay is formedbetween the surrounding depression 11 and the radially adjacent part ofthe annular space 12. It forms the static flexible element 5. The tool1, as a result of this annular stay-shaped element 5, can carry outrelatively large movements relative to the tool holder 2 when radiallyloaded. The shaft end accordingly performs a relatively large movementso that the damping element in the form of the described oildisplacement system 12, 18 can be provided in the receptacle 3 of thetool holder 2. The pressure medium 13 which is present in the annularspace 12 as well as in the damping gap 18 provides an excellent dampingaction. As a result of the described elastic tool fixing device with itshigh damping action, chatter vibrations of the tool 1 can be suppressedexcellently. The tool fixing device is excellently suitable for slimtools which, because of their minimal flexural strength and systemdamping action, often perform during machining great vibrationamplitudes which occur in the form of regenerative chatter. The use ofthe described tool fixing device allows great cutting depths of the tool1 without risking a chatter tendency. The tool fixing device is alsoexcellently suitable for boring operations with tools 1 in the form ofboring bars having a length/diameter ratio >4. Since a chatter tendencydoes not occur as a result of the elastic and damped tool fixing device,the efficiency of such long and thin boring bars is not impaired.

Instead of the described pressure medium displacement system, the shaftend in the receptacle 3 of the tool holder 2 can also be surrounded byat least one rubber element and the like as a static flexible element.An excellent damping action can also be achieved with such mechanicalcomponents.

Even though the elastic tool fixing device results in a reduced totalstatic strength at the tool tip in the radial direction, the resonanceincrease can be considerably reduced, for example, by a factor 5 to 50,by means of a corresponding adjustment of the clamping strength anddamping action between the tool holder 2 and the tool shaft 4.

When in the case of special requirements, for example, with respect tonarrow dimensional tolerances for the machining carried out by the tool1, the increased static yielding action as a result of the elasticclamping action is not permissible during machining of the tool 1, theyielding of the fixing device can be eliminated if needed; however, theadvantage of the increased damping action is no longer provided. FIG. 4shows an embodiment for such of configuration of the elastic tool fixingdevice. The sleeve 9 is shorter than in the previous embodiment and hasa conical mantle 20 whose diameter increases steadily in the directiontoward the flange 10 of the sleeve 9. Accordingly, between thecylindrical inner wall of the receptacle 3 of the tool holder 2 and thesleeve 9 an annular space 12 is formed which tapers in the directiontoward the flange 10 and in which the pressure medium 13, preferablyoil, is present. This annular space 12 is closed in the direction towardthe bottom 14 of the receptacle 3 by an axially adjustable cone sleeve21. It rests with its cylindrical outer mantle 22 against the inner wallof the receptacle 3. It has a central depression 23 in its end facefacing the sleeve 9 which conically widens in the direction toward thesleeve 9 and surrounds a matching conical projection 24 of the sleeve 9at a minimal spacing. Between this projection 24 and the sidewall andthe bottom of the depression 23 a gap-shaped damping space 25 is formedwhich is connected to the annular space 12. Accordingly, the pressuremedium 13 is also present in the damping gap 25.

The cone sleeve 21 is fastened on a support 26 which is provided at thefree end of an adjusting rod 27. It projects into the receptacle 3 andextends through the tool holder 2. The adjusting rod 27 can be axiallydisplaced by a drive (not illustrated). By doing so, the width of thecone-shaped damping space 25 can be adjusted. When the cone sleeve 21 ismoved upwardly from its position according to FIG. 4, the width of thecone-shaped damping gap 25 will increase. Accordingly, the dampingaction, which is provided by the pressure medium contained therein, isreduced; however, the total system damping action increases thereby.When the adjusting rod 27, in the illustration according to FIG. 4, ismoved in the downward direction the gap width of the damping gap 25 isreduced. It can be reduced to such an extent that the shaft end isfixedly clamped in the tool holder 2. Accordingly, by means of theadjusting element in the form of the cone sleeve 21, the system dampingaction can be adjusted optimally with regard to a particularapplication, respectively. When during machining, for example, duringprecision machining, a rigid fixation of the tool 1 in the tool holder 2is required, the upper tool end can be fixedly clamped by acorresponding reduction of the gap width of the damping gap 25 towardzero.

The two embodiments according to FIGS. 3 and 4 show the flange 10 of theclamping sleeve 9 sealed relative to the tool holder 2. The pressuremedium 13 is preferably a hydraulic medium which is present in theclosed space 12, 18, 25 or which can be supplied by the machining device(not illustrated) via bores (not illustrated). The tool holders 2 areeach provided with a grab groove 28 for a tool changer.

FIG. 5 shows a comparison of the essential differences between the knownstandard tool fixation device without any damping action and thedescribed damped tool fixation device.

In the upper illustration the step response is illustrated in a diagram.In the undamped tool fixing device the tool (original tool) performsgreat vibrations during machining which subside only slowly. Theseun-damped vibrations result in the disadvantageous chatter of the toolduring machining. Completely different conditions are present for thedamped tool fixation device. The vibrations of the damped tool subsidevery quickly so that the risk of chatter of the tool, even if it is verylong and slim, can be reduced considerably during machining.

In the un-damped tool fixing device a very strong resonance increaseresults for the tool, while for a tool which is mounted in a dampedfashion the resonance ratio is greatly reduced (FIG. 5, center).

According to the reduction of the resonance ratio, the negative realcomponent of the flexibility locus curve for the damped tool fixingdevice in comparison to the undamped fixation device is significantlyreduced. Since the cutting depth that is possible without chatter isreverse-proportional relative to the negative real component (FIG. 5,bottom), an enormous efficiency increase results by means of the dampedtool fixing device which increase is greater by a factor 5 to 10 in theillustrated embodiment in comparison to a tool that is clamped withoutdamping.

What is claimed is:
 1. A tool fixing device for clamping a tool in atool holder, wherein the tool holder has a receptacle configured tofixedly clamp a shaft of the tool, said tool fixing device comprising atleast one static flexible element inserted into a force flow between thetool and the tool holder and configured to damp tilting and bendingvibrations of the tool, further comprising a clamping sleeve configuredto be inserted into the receptacle of the tool holder, wherein said atleast one static flexible element is provided at least partially in saidclamping sleeve.
 2. The fixing device according to claim 1, wherein saidat least one static flexible element has a springy clamping location. 3.The fixing device according to claim 1, wherein said clamping sleeve hasa weakened wall portion forming an articulation.
 4. The fixing deviceaccording to claim 3, wherein said weakened wall portion is an annularstay of said clamping sleeve.
 5. The fixing device according to claim 1,further comprising at least one damping element arranged in thereceptacle and configured to act on an end of the shaft of the toolinserted into the receptacle.
 6. The fixing device according to claim 5,wherein said at least one damping element is a squeeze-film damper. 7.The fixing device according to claim 5, wherein said at least onedamping element is an elastic rubber ring.
 8. A tool fixing device forclamping a tool in a tool holders wherein the tool holder has areceptacle configured to clamp a shaft of the tool, said tool fixingdevice comprising: at least one static flexible element inserted into aforce flow between the tool and the tool holder and configured to damptilting and bending vibrations of the tool; at least one damping elementarranged in the receptacle and configured to act on an end of the shaftof the tool inserted into the receptacle; wherein said at least onestatic flexible element is a spring element.
 9. A tool fixing device forclamping a tool in a tool holder, wherein the tool holder has areceptacle configured to clamp a shaft of the tool, said tool fixingdevice comprising: at least one static flexible element inserted into aforce flow between the tool and the tool holder and configured to damptilting and bending vibrations of the tool; at least one damping elementarranged in the receptacle and configured to act on an end of the shaftof the tool inserted into the receptacle; wherein said at least onedamping element comprises a pressure medium.
 10. The fixing deviceaccording to claim 9, wherein said pressure medium is a hydraulic oil.11. The fixing device according to claim 9, comprising a clamping sleeveconfigured to be inserted into the receptacle of the tool holder suchthat a space is formed between said clamping sleeve and the receptacleand said space surrounds said clamping sleeve, wherein said pressuremedium is arranged in said space surrounding said clamping sleeve. 12.The fixing device according to claim 11, wherein said at least onedamping element comprises a damping gap and wherein said space isconnected to said damping gap.
 13. The fixing device according to claim12, wherein said damping gap has an adjustable width.
 14. The fixingdevice according to claim 13, wherein said damping element comprises apressure member configured to adjust said adjustable width of saiddamping gap.
 15. The fixing device according to claim 14, wherein saiddamping element further comprises an adjusting rod connected to saidpressure member, wherein said adjusting rod penetrates the tool holderand is configured to act axially on said pressure member for adjustingthe width of said damping gap.